a. Field of the Invention
The present invention generally relates to optical systems, and more particularly to providing reference illumination sources within such optical systems.
b. Background of Invention
Optical metrology and inspection equipment such as reflectometers may often use high power optical lens/objectives in close proximity to surfaces for measurement and/or inspection purposes. In manufacturing environments these surfaces may often release gases or vapors that can coat the lens/objectives in such a manner that light collected by these lens/objectives is distorted. The measurement and/or inspection results are thus distorted.
Metrology and inspection equipment may contain external illumination reflection reference surfaces which are assumed to be stable and used to control the illumination received by the lens/objectives. However, since these reference surfaces are also susceptible to released gases and vapors, the reference illumination levels generated by the reference surfaces become distorted. This distortion subsequently unduly influences the measurement or inspection of the surface.
It may, therefore, be advantageous, among other things, to generate reference illumination surfaces that are at least to some extent independent of contaminants associated with a system.